Machine-to-machine (M2M) information and data exchange between machines over a wireless network, and is an important direction for next-stage development of mobile communications. The M2M is widely applied to many fields that include intelligent transportation, a building control system, a smart home control system, a video surveillance system, industrial monitoring, and the like.
In an M2M system, when downlink data in a core network needs to be sent to user equipment (UE), a core network device starts a paging timer and sends, to each base station in a paging area, a paging message that carries a UE identifier (ID). When receiving the paging message, the base station in the paging area calculates, according to the UE identifier carried in the paging message, a nearest paging occasion (PO), at an air interface, of the UE corresponding to the UE identifier, and sends, when the PO arrives, the paging message to the UE corresponding to the UE identifier. The UE corresponding to the UE identifier initiates a random access process after receiving the paging message, to establish a connection to the base station and the core network. The downlink data is sent to the UE over the core network after the UE accesses the network. A paging moment depends on a paging super frame (PSF) and the PO.
To save power of the UE in an idle state, an extended discontinuous reception (eDRX) mechanism is introduced into the M2M system. The UE in the idle state listens on a paging channel in an eDRX manner. That is, the UE listens on the paging channel only when a paging moment of each eDRX active period arrives. If no paging message is obtained by listening, the UE enters a sleep state and wakes up when a next paging moment arrives to listen on the paging channel. In this way, power consumption of the UE is reduced. Specifically, the UE maintains a UE-specific eDRX cycle, and the UE reports the eDRX cycle to the core network device by using a NAS message or in another manner. When delivering a paging message, the core network device adds information such as the eDRX cycle and the UE identifier to the paging message, and delivers the paging message to a base station. The base station calculates a paging super frame (PSF) and a PO of the UE according to the information, and sends the paging message at a paging moment that is indicated by the PSF and the PO. The UE calculates the PSF and the PO according to information such as the eDRX cycle of the UE and the UE identifier, and receives the paging message at the paging moment that is indicated by the PSF and the PO. The PSF and the PO that are calculated by the UE need to be the same as the PSF and the PO that are calculated by each base station. The PSF is a super frame that has a PO, and the PO is a frame that is in the paging super frame and that has a paging message.
The inventors find that the existing paging method has the following problems: In consideration of mobility of the UE, if the UE in the idle state moves between different cells, the UE may perform cell reselection before a paging moment of a current cell arrives, a new cell is reselected, and a paging moment of the new cell has passed when reselection is completed. Therefore, the UE misses the paging moment of the current cell, and also misses the paging moment of the new cell. After cell reselection, the UE can receive the paging message only when a paging moment of a next eDRX cycle arrives. In the M2M system, the eDRX cycle is as long as one or more hours. After the new cell is reselected, the UE may need to wait almost one eDRX cycle before the next paging moment arrives. Due to the relatively long time wait, the UE is very likely to perform cell reselection again in this period of time, and also misses an oncoming paging moment of the current cell. After a new cell is reselected, the UE may also miss a paging moment of the new cell, and so on. If the UE keeps moving, cell reselection may occur continually during the wait. Consequently, the UE repeatedly fails to obtain a paging moment, and cannot receive the paging message.